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Effect of Slight Misorientation of Sapphire Substrate on Metalorganic Chemical Vapor Deposition Growth of GaN

The effects of slight misorientation from c-plane sapphire (α-Al2O3) substrates on GaN surface morphologies and electroluminescence (EL) properties were studied. The GaN layers were grown using a two-step growth method under atmospheric pressure by metalorganic chemical vapor deposition (MOCVD). When using around 0.17° misoriented sapphire substrate tilted toward both directions, a small step-type morphology appeared. On the other hand, using c-plain substrate or substrates with the misorientation angle larger than approximately 0.25° from the c-plane, a scale-shaped morphology appears. We also found that the misorientation of the substrate significantly affects the uniformity of the EL image. On the other hand, the light output powers of the light-emitting diodes (LEDs) fabricated on the substrates with different misorientations were almost the same in spite of the different surface morphologies.

Pendeoepitaxy of GaN on sapphire substrate with SiO2 mask is demonstrated and characterized by transmission electron microscopy and double crystal x-ray diffraction. A continuous layer of GaN with low dislocation density was achieved by this method. Parts of the GaN layer are tilted symmetrically toward direction and have two kinds of coalesce and tilt boundaries. Each boundary was formed by a vertical array of piled up dislocations with the Burger’s vector of. The tilting mechanism in pendeo-epitaxy is discussed in terms of surface interaction between the SiO2 mask and ELO-GaN.


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